It is generally known to install in motor vehicles running on wheels additional crawler undercarriages between the steered axles and the unsteered axles to reduce the load pressure on the ground and/or to enhance off-road performance. In the context of the following description, the crawler undercarriage also includes crawler chains and crawlers, i.e., motor vehicles with additional undercarriages where the wheels for reducing the load pressure on the ground run on crawler chains. Such arrangements are particularly useful for off-road vehicles, construction vehicles, agriculture and forest management vehicles, and also for transport vehicles, mobile homes and in military vehicles.
In these vehicles, crawler undercarriages were installed to address different applications and solve different problems and to make wheeled vehicles suitable for off-road use. The switch-over to the crawler undercarriage and activation of the crawler undercarriage can be accomplished in many different ways, but still poses problems and needs improvement.
The invention disclosed in DE-OS 20 26 295 provides a crawler undercarriage of the aforedescribed type which makes it possible to quickly convert road vehicles to vehicles for off-road driving in snow and the like, without requiring substantial changes on the vehicle itself. After removal of the crawler undercarriage, the vehicle should again be usable as a road vehicle.
At the same time, the crawler undercarriages should be as wide as possible to improve off-road performance.
To solve this problem, a crawler undercarriage with a clutch was proposed that is applied to the driving wheel and at least partially supports the undercarriage. The clutch can be attached on the driven disk wheel of the vehicle instead of a wheel rim with the same mounting hardware. With a crawler undercarriage of this type, the rims of the driven wheels of the vehicle, for example of a passenger car, are removed and the clutch of the crawler undercarriage is screwed in place. The drive of the vehicle powers the driving wheel of the crawler vehicle via this clutch, with the entire vehicle now being driven via the crawler undercarriage.
Although this changeover to a tracked vehicle should be quick and not require changes on the vehicle, the vehicle must still be stopped and shut down, because the changeover is manual.
DE-OS 27 35 389 discloses a simpler concept of a wheeled vehicle with a crawler chain, which is only operated when the vehicle drives across impassable terrain.
A freely retractable crawler chain with a suitable power source is installed, wherein the crawler chain is installed on the vehicle frame approximately midway between the front wheels and the rear wheels. The crawler chain that is installed between the front wheels and the wheel wheels of the vehicle can rotate and be pulled up against the vehicle frame. The power source is independent of the driving wheels, when the crawler chain is raised and not in contact with the road surface. Conversely, the drive source is coupled to the driving wheels when the crawler chain is lowered and in contact with the road surface.
This arrangement obviates the need for a complex manual changeover and an interruption of the driving operation, but power transfer to and retraction of the crawler chain is still relatively complex.
DE-OS 28 11 675 proposes an additional crawler chain undercarriage for motor vehicles, which can be easily installed on the vehicle, in particular on off-road vehicles such as jeeps and the like, at a later date, or during manufacture. The additional drive is configured for bilateral use on both sides of the vehicle frame and can operate as an independently actuated lifting, supporting or vehicle stabilization element.
As also disclosed in DE-OS 28 11 675, each drive assembly of this type which is formed of a crawler chain, guide rollers, a roller yoke and a resiliently supported chain roller guide, is fixedly, but independently, connected with the respective side of the vehicle frame via an auxiliary frame forming a support structure. In one embodiment, the crawler chain is formed as a tensionable, flexible belt or as a link chain with a patterned surface. The guide rollers are identical or have different stepped roller diameters. The roller guides are mounted on the auxiliary frame by either hydraulic or mechanical elements, such as guide pins, guide bushings and spring elements, and are secured in their final position by rods and other standard, commercially available safety elements.
However, the hydraulic and mechanical actuators for the additional device are difficult to install and to manufacture due to their special design.
DE 38 43 532 A1 discloses additional crawler pairs that can be moved vertically underneath a chassis frame to improve traction. The purpose is here to provide an off-road vehicle and road vehicle that employs pairs of wheels or crawlers depending on the situation, whereby the undercarriage lacks a dedicated drive. This concept only applies to drawn/pulled transport vehicles although the actual drive concept is hereby unimportant.
DE 40 33 147 A1 discloses a multipurpose vehicle with additional crawler undercarriage for motor vehicles, wherein the additional crawler undercarriage includes an additional braking system, an additional integrated direction-reversing device, and an extension device to raise the actual vehicle from the ground.
Although the vehicle is intended for general use, this arrangement is complex to implement, because the additional crawler undercarriage requires a support structure with drive shafts, bearings and additional rollers, a pair of specially designed continuous crawlers, a steering connection installed in the center of the support structure, and so-called actuating devices which may include power transmission, reversing mechanism, pressure cylinders, valves and associated hydraulic controls.
It therefore appears beneficial to return to the original objective and to simplify the design of both the drive mechanism and the provisioning of additional crawler undercarriages.
For example, DE-OS 27 53 706 discloses as a potential solution a Rakett running gear. However, this approach does not optimize the drive mechanism.
DE 195 19 670 A1 suggests converting tracked vehicles into simple road vehicles, but the proposed solution is also complex.
The drive system disclosed in DE 39 10 263 A1 which employs a coupling element between rotating and linear movement for driving an additional running gear also requires specially manufactured components.
DE 690 14 772 T2 discloses a motor vehicle for road and off-road use, which can be used for surveying, exploration or drilling activities. The vehicle has an auxiliary frame with crawlers arranged between the wheels and includes individually actuatable lifting cylinders. The auxiliary frame can be lowered sufficiently to raise the wheels off the ground. The lifting cylinders can hold the vehicle in a desired horizontal position while resting on the crawlers. The auxiliary frame can optionally be mounted underneath an existing vehicle.
The approach disclosed in DE 690 14 772 T2 not only enhances the mobility with the crawlers, but also provides a level and stable support for the vehicle during certain specialized operations. Nor does this approach suggest to arrange additional extendable and retractable crawler undercarriages between the steered and unsteered wheel axles in a mass-produced motor vehicle by, for example, retrofitting the vehicle with an additional mechanically simple and low-cost crawler undercarriage, with a low installation height. DE 690 14 772 T2 also does not show a way how the additional crawler undercarriage can be retracted and extended without impairing the operation of the original motor vehicle, or how to efficiently drive the additional crawler undercarriage with the existing drive components of the motor vehicle, how to assemble the additional crawler undercarriage at low-cost from standardized production components, and how to power the additional crawler undercarriage efficiently and effectively from the motor vehicle.
It is therefore an object of the invention to provide a drive system for motor vehicles with extendable and retractable additional crawler undercarriages arranged between the steered and unsteered wheel axles, which obviates the disadvantages of the prior art and makes possible to retrofit a mass-produced motor vehicle with a simple and cost-effective additional crawler undercarriage, to retract and extend the additional crawler undercarriage without impairing the operation of the existing motor vehicle, to maintain the original ground clearance of the vehicle, to employ the existing drive elements of the vehicle for the additional crawler undercarriage, to assemble and procure the additional crawler undercarriage cost-effectively from standard components manufactured in series, and to transfer power from the motor vehicle to the additional crawler undercarriage with high-efficiency and economically.